Modern wireless telephone systems can provide a normal voice-grade connection to a vehicular mobile or portable handset through well-known telephony techniques. Wireless telephone systems have typically evolved to incorporate automated answering machine techniques, such as voice-mail, allowing a caller to deposit a message when the mobile unit or handset is out of range of the system. Cordless telephone systems, used primarily in residences, have similarly evolved to incorporate answering machines for deposit of voice messages when a person does not answer the telephone.
Popularly, such commercial and private systems operate by notifying the user that a message has been deposited, such as by an interrupted tone in the handset earpiece or visibly flashing of an annunciator on the handset or base unit Retrieval of the deposited message by the user is, then, either directly through a speaker in the base unit in the cordless phone case or by playback from the voice-mail server through the handset over a normal voice connection in the commercial cellular phone case. Voice-mail systems also can attempt to deliver a message to a specified alternative destination upon deposit or after some pre-determined period of time through well-known store-and-forward messaging techniques. Rudimentary forms of store-and-forward schemes have been employed for delivery of answering machine messages over the switched telephone network by out-dialing another telephone and offering the answering party the voice mail, especially if a passcode is entered.
A limitation of prior art wireless telephone messaging systems has been an inability to discriminate between poor inbound link performance and poor outbound link performance. For normal voice connections symmetric performance is highly desirable and the distinction between outbound performance from the base and inbound performance from the handset is irrelevant, since both must be acceptable for normal voice. Simple delivery of voice mail, however, requires only minimal inbound performance with less than perfect outbound performance. Other limitations of prior art messaging systems include an inability to convey the deposited voice mail to the handset automatically and independently of the user when the handset is once again in-range, or to convey at a rate sustainable by a link unacceptable for normal voice connections, or to defer delivery spreading it during low-traffic periods to increase overall efficiency. Voice mail can only be retrieved in commercial systems by requesting it from the handset after having set up a normal symmetric bandwidth connection and not at all from cordless handsets since retrieval is directly from the base unit. Operations such as these have worked reasonably well for many commercial systems, but do not make efficient use of the inbound spectrum and unnecessarily deplete handset battery-energy to make a symmetric connection. Users, both cellular and cordless, also are denied an additional convenience by not having deposited messages readily available at the handset, even when not sufficiently in-range to receive or place calls.
Thus, what is needed is a method and apparatus for accepting voice mail at a base unit and conveying voice mail to a mobile unit in a wireless telephone system. Preferably, the method and apparatus will not affect the low-latency characteristics of prior art systems, but will make use of high efficiency store-and-forward messaging techniques, adding a significant degree of convenience by making voice mail messages available at the mobile handset without a symmetric bandwidth connection, while economizing battery energy usage for the inbound portion of the link.